1. Field of the Invention
The present invention relates to an apparatus for detecting the earthed side of an AC power supply.
2. Description of the Prior Art
In Japan and certain other countries and regions, the single-phase two-wire system is adopted for the power supplies of general households and those of general office buildings. Electric equipment utilizing the power supplies are used without having their housings and grounds earthed, except in special cases.
Meanwhile, particularly personal computers are often produced in foreign countries and regions and then imported to Japan. Such products are manufactured premising the single-phase three-wire system, and are furnished as a standard with power supply plugs each having three pins (hereinbelow, also termed xe2x80x9c3Pxe2x80x9d).
In Japan etc., however, a plug socket for the power supply specification of the single-phase two-wire system is for a plug of two pins (xe2x80x9c2Pxe2x80x9d), and the equipment is used inevitably by attaching a conversion adaptor for the 2P plug, to the 3P plug in order to feed a supply voltage to the equipment. Accordingly, a ground line originally laid in the equipment is in a floating state.
In this manner, the ground line has heretofore been in the floating state, and it has therefore been impossible to prevent unfavorable electromagnetic waves from leaking out.
Besides, although either of the lines of the AC power supply is earthed, general users cannot know which of the terminals of the plug socket is the terminal of the earthed side.
The present invention has been made in view of the problems stated above, and it has for its object to provide a detection apparatus for detecting the earth-side power supply line of an AC power supply so that an electric equipment can be readily earthed by connecting the ground thereof to the earth-side terminal of the power supply.
In order to solve the problems stated above, the present invention has taken technical measures to be explained below.
The present invention features a detection apparatus for detecting a line on an earthed side of an AC power supply, comprising power supply terminal means which can be connected to the AC power supply; ground terminals which can be connected to ground of an electric equipment (including an electronic equipment); a switching unit which selectively connects either of AC lines connected with the AC power supply, to ground of the detection apparatus, the selective connection being changed-over; an antenna unit which detects an electromagnetic wave; and a discrimination unit which discriminates an earthed side and a non-earthed side of the AC lines on the basis of a discrepancy of levels of the electromagnetic wave as depend upon which of the AC lines is connected to the ground of the detection apparatus.
Besides, the discrimination unit should preferably be fed with a signal in which the electromagnetic wave signal detected by the antenna unit is superposed on a main signal that is not affected by noise from th e AC power supply.
Here, mentioned as the signal which is not affected by the noise from the AC power supply is, for example, a signal which is generated by a power supply (for example, dry cell) separate from the AC power supply, or a signal which is generated using a voltage charged in a capacitor.
In addition, the detection apparatus should preferably include, at least, the decision unit inside a housing; the housing being provided with a switch which is relevant to the operation of the detection apparatus; the antenna unit being arranged in the vicinity of the switch. In this case, the electromagnetic wave can be detected with ease.
More concretely, the antenna unit should preferably be disposed inside the housing and behind the switch.
Besides, it is preferable that the switch is mounted on a circuit board disposed inside the housing, so as to be manipulatable from outside the housing, and that the antenna unit is formed on the circuit board.
Although the switch may be any switch relevant to the operation of the detection apparatus, it should preferably be a detection starting switch which commands the discrimination unit to start the detection.
Further, the main signal should preferably be generated by manipulation of the detection starting switch.
Besides, the power supply terminal means should preferably be a plug of two pins as can be inserted into a plug socket. Also, the detection apparatus should preferably comprise a housing including a plug socket unit into which a power supply plug of the electric or electronic equipment can be inserted.
Further, it is preferable that the housing is attached to a building or a house, and that the power supply terminal means is connected to AC-power-supply wiring lines laid in the building or the house.